Information storage devices are in wide spread use, and are used to store and retrieve large amounts of data. Such information storage devices generally include a rigid media for storing information, a read/write device for creating and accessing the information, and an actuator assembly for positioning the read/write device over the rigid media. One common example of such an information storage device is a hard disk drive having one or more rotating magnetic disks, over a surface of each of which a head suspension and a head slider are positioned. Each of the head suspensions is attached to an actuator arm of the actuator assembly, and the actuator assembly thus positions the suspensions and sliders at a desired location over the rotating disks.
A conventional actuator assembly in a hard disk drive includes an actuator block, one or more arms extending from the actuator block, and a plurality of head suspensions that are mounted to the arms of the actuator block. The actuator block and arms extending from the block are typically machined from a single piece of starting material, such as aluminum, and are typically referred to as an E-block. The number of arms on the E-block and the number of head suspensions in the actuator assembly are usually dependent on the number of disks in the disk drive, with a head suspension positioned over each magnetic surface of the individual disks. Each head suspension is typically mounted to an arm of the E-block by swaging or ball staking a vertical swage boss extending from a base plate on an end of the head suspension to the arm. In this method, the swage boss is inserted in a hole in the arm and is then deformed to engage the arm by forcing a round ball through the boss. The E-block is coupled to a rotary actuator within the disk drive, and in this manner, the head suspensions can be positioned over a desired location of the disks.
E-blocks having suspensions mounted to the arms of the block have certain disadvantages, however. Increased spacing between the suspensions is typically required to accommodate the height of the vertical swage boss. In addition, a large vertical force must be used to swage the boss to the actuator arm, which can warp or otherwise permanently deform the actuator assembly. Suspensions that are swaged to the actuator block also cannot easily be selectively reworked or replaced due to the nature of the swaging process.
In recent years, integral arms comprising an actuator arm and a head suspension have been introduced into the disk drive industry to address these disadvantages. In such an embodiment, a head suspension is formed integral with an actuator arm from a single piece of material, and the integral arm is mounted over the outer sleeve of an actuator spindle assembly, such as for example by inserting the spindle through an aperture at a proximal end of the integral arm. The spindle assembly is coupled to an actuator, and the actuator positions the integral arm over a desired location of a disk. Because the suspension is formed integral with the actuator arm, an integral arm does not require additional spacing for a swage boss tower, and the arm is not deformed by the large forces required to swage the suspension to the arm. An integral arm also typically has less mass and inertia than an E-block/head suspension combination, which can increase the response time for positioning the head suspension over the disk.
Actuator assemblies can be formed having a stacked array of integral arms to access data stored on a plurality of disks within an information storage device. In such a stacked array, a spindle assembly is inserted through the aperture of a bottom integral arm, and a spacer is placed over the spindle assembly. A stacked array can be formed by placing the aperture of a second arm over the spindle assembly, and a third arm can be placed back-to-back with the second arm in a similar fashion. A spacer can be inserted between the second and third arms if desired, and additional arms and spacers can be added to the spindle as necessary for a specific application. After the desired numbers of arms are inserted over the spindle assembly, a washer and lock nut can be placed on the spindle assembly and tightened to provide an axial compressive force that frictionally secures the arms and spacers to the actuator spindle assembly.
U.S. Pat. No. 5,495,375 discloses a particular spindle assembly. Among other components, the disclosed spindle assembly includes an outer sleeve, a washer, and a nut. It would be preferred that such components were not required.
It is important that the individual arms of the actuator assembly be positioned at the appropriate height (commonly referred to as the Z-height) above an associated disk in the information storage device. In this regard, the arms must be mounted to the actuator spindle assembly at the appropriate location. Unfortunately, the arms on the spindle are dislocated from optimal by the stack up of the height variation of each component, for example the spacer or the arms.
There is therefore a continuing need for an actuator assembly that securely holds head suspensions in place as the actuator rotates, reduces the stack up tolerances being placed all on the top arm assembly, and provides more consistent Z-height variation among all the flying heads. An actuator assembly that provides accurate Z-height spacing of the head suspensions while also reducing the component count and hence cost would also be highly desirable.